Electrically controllable integrated switch

ABSTRACT

Methods of forming and operating a switching device are provided. The switching device is formed in an interconnect, the interconnect including a plurality of metallization levels, and has an assembly that includes a beam held by a structure. The beam and structure are located within the same metallization level. Locations of fixing of the structure on the beam are arranged so as to define for the beam a pivot point situated between these fixing locations. The structure is substantially symmetric with respect to the beam and to a plane perpendicular to the beam in the absence of a potential difference. The beam is able to pivot in a first direction in the presence of a first potential difference applied between a first part of the structure and to pivot in a second direction in the presence of a second potential difference applied between a second part of the structure.

This application is a divisional of U.S. application Ser. No.14/286,331, filed on May 23, 2014, which claims the benefit of FrenchApplication No. 1355221, filed on Jun. 6, 2013, which application ishereby incorporated herein by reference.

TECHNICAL FIELD

The invention relates to integrated circuits and, in particularembodiments, to switching devices such as breakers or switches, such aselectrically activatable switching devices.

BACKGROUND

Currently, the switching devices produced within integrated circuits aregenerally switches of the electromechanical microsystem (MechanicalElectro Micro System or MEMS) type using elements made, for example, ofpolysilicon. However, the technology used to produce such switches is adedicated technology, which is difficult to integrate into a CMOSstandard technological flow.

SUMMARY

According to one embodiment, there is proposed a new switching devicethat can be integrated into all CMOS technological flows through thepossible addition of just a few extra operations (the addition of a masklevel, for example), doing so without using the conventional technologyof MEMS type.

According to one embodiment, there is also proposed a switching devicethat exhibits a bilateral planar movement and that is almost, or indeedtotally, insensitive to temperature variations as well as to stressesgenerated during its fabrication.

According to one aspect, there is proposed an integrated circuitcomprising above a substrate an interconnection part comprising severalmetallization levels separated by an insulating region. Such aninterconnection part is commonly designated by the person skilled in theart under the acronym “BEOL” (“Back End Of the Line”).

According to a general characteristic of this aspect, the integratedcircuit furthermore comprises, within the interconnection part, anelectrically activatable switching device comprising, in a cavity of ahousing, at least one assembly including a beam held by a structurebuilt into the housing, the beam and the structure being metallic andsituated within one and the same metallization level.

The locations of fixing of the structure on the beam are arranged so asto define for the beam a pivot point situated between these fixinglocations.

The structure is substantially symmetric, to within fabricationinaccuracies, with respect to the beam and with respect to a planeperpendicular to the beam, in the absence of a potential differenceapplied to the structure.

Moreover, the beam is able to pivot in a first direction in the presenceof a first potential difference applied between a first part of thestructure and to pivot in a second direction in the presence of a secondpotential difference applied between a second part of the structure.

Such a switching device is thus produced in the so-called BEOL part ofthe integrated circuits within one and the same metallization level, andtherefore exhibits an essentially two-dimensional and metallicstructure. It is therefore readily integrated into a CMOS technologicalflow by making ample use of the conventional production steps for theBEOL part of the integrated circuit.

Moreover, the structure being substantially symmetric, to withinfabrication inaccuracies, ideally with respect to a point substantiallycoinciding with the pivot point, it is almost insensitive or indeedtotally insensitive to temperature variations since, in the presence ofsuch temperature variations, the possible expansions or contractions ofthe structure are distributed symmetrically with respect to the beam,thus giving rise to almost no displacement of this beam.

Initially, the assembly, and in particular the structure, isencapsulated in an insulating material packing the cavity of thehousing. After de-encapsulation, that is to say removal of thisinsulating material, making it possible to release the assembly, thesymmetric character of the structure makes it possible to confer anidentical geometry on the assembly before and after encapsulation.Moreover, after de-encapsulation, the structure is advantageouslystressed in tension in the absence of any potential difference appliedto itself. In addition, the tension-stressed character of the structurewill favor the pivoting of the beam upon the application of the first orof the second potential difference.

The structure is advantageously X-shaped, the first part of thestructure to which the first potential difference is applied comprisinga first branch of the X, and the second part of the structure to whichthe second potential difference is applied comprising the other branchof the X.

According to one embodiment, the assembly of the switching devicefurthermore comprises, in the housing, at least one abutment situatedsome distance from the beam in the absence of potential differenceapplied to the structure and designed to be in contact with the beamupon the application to the structure of one of the two potentialdifferences.

It is then possible to produce a current limiter or else a currentintensity detector. As a variant, the assembly of the switching devicecan furthermore comprise in the housing a first abutment and a secondabutment, both situated some distance from the beam in the absence ofpotential difference applied to the structure. The first abutment isdesigned to be in contact with the beam upon the application to thestructure of the first potential difference, and the second abutment isdesigned to be in contact with the beam upon the application to thestructure of the second potential difference.

With this embodiment, it is then possible to obtain a current limiter ora current intensity detector assigned to two distinct parts of theintegrated circuit which would not be in operation simultaneously.

Other embodiments of the assembly are possible.

In the case where at least one wall of the housing comprises an opening,it is particularly advantageous, but not indispensable, especially inorder to reduce the risk of degradation of the external environment ofthe housing, that the integrated circuit furthermore comprises a means,for example a metallic plate, external to the housing, and configured soas to form an obstacle to a diffusion of fluid out of the housingthrough the opening, typically during the de-encapsulation of theassembly encapsulated in the housing.

In addition, when provision is made for a metallization intended tocontact a part of the assembly by passing through an opening made in awall of the housing, the metallization then advantageously passesthrough the external means, for example the metallic plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics of the invention will becomeapparent on examining the detailed description of wholly non-limitingembodiments and of the appended drawings in which:

FIG. 1 schematically illustrates an embodiment of an integrated circuitaccording to the invention;

FIG. 2 illustrates in greater detail but still in a schematic manner, anembodiment of an assembly of a switching device according to theinvention;

FIG. 3 schematically illustrates an assembly of the prior art housed ina cavity of a housing before and after release of this assembly; and

FIGS. 4 to 16 relate to various embodiments of an integrated circuitaccording to the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In FIG. 1, the reference CI designates an integrated circuit withinwhich will be produced a switching device DIS comprising an assembly 1housed in a cavity CV of a housing LGT.

As will be seen in greater detail hereinafter, the metallic device DISand the housing LGT are produced within several metallization levels(here three metallization levels M2, M3, M4, and two levels of vias V2,V3) of the interconnection part RITX of the integrated circuit CI, thisinterconnection part commonly being designated by the person skilled inthe art under the acronym BEOL (“Back End Of the Line”).

This interconnection part is situated above the substrate SB of theintegrated circuit and above the components, such as transistors T,produced in and on the substrate SB.

As is conventional in this respect, some of the metallic tracks producedwithin the various metallization levels of the integrated circuit areinterlinked by interconnection holes or vias, the assembly of thesetracks and vias being encapsulated in an insulating region RIS, whichcan be formed of one or more electrically insulating materials.

The housing LGT comprises especially a lower part PI produced at themetal level M2, a lateral wall PLD produced at the via level V2, at themetal level M3 and at the via level V3, as well as another wall PLG alsoproduced at the via level V2, at the metal level M3 and at the via levelV3.

The housing LGT is closed by a holed cap CPT comprising several orificesOR. The cap CPT is produced at the metal level M4.

As will be seen in greater detail hereinafter, the assembly 1 isinitially encapsulated in the insulating material RIS of theinterconnection part RITX and then, subsequently, after removal of thismaterial RIS from the cavity CV of the housing, released.

FIG. 2 is a view from above of the metal level 3 illustrating in greaterdetail an exemplary embodiment of the assembly 1.

The housing LGT comprises, in addition to the wall PLD and the wall PLG,two other walls PLA and PLF. The assembly 1 comprises a structure STRand, here, two fixed abutments or contact regions BT1 and BT2.

The structure STR is here a symmetric X-shaped structure pivotablyholding a beam PTR. The structure STR and the beam PTR are produced atthe same metallization level, in this instance the metallization levelM3.

In FIG. 2, the beam PTR is in a rest state in which its end is somedistance from the contact regions BT1 and BT2.

This rest state is obtained, after de-encapsulation of the assembly 1,in the absence of any potential difference applied to the structure STR.

On the other hand, as will be seen in greater detail hereinafter, uponthe application of a potential difference to a first part of thestructure, typically a first branch of the X, the beam PTR will pivot soas to come into contact with one of the abutments, for example thecontact region BT1.

In addition, upon the application of another potential difference toanother part of the structure, typically the other branch of the X, thebeam PTR will pivot in the other direction so as to come into contactwith the contact region BT2.

In order to avoid short-circuits at the level of the walls of thehousing upon the application of the various potential differences, thewall PLA comprises two wall pieces PLA1 and PLA2 separated by a spaceESPA.

Likewise, the wall PLF comprises two wall pieces PLF1 and PLF2 separatedby a space ESPF.

The contact regions BT1 and BT2 are respectively built into two wallpieces PLG1 and PLG2 of the wall PLG, these two wall pieces PLG1 andPLG2 being separated by a space ESPG.

Finally, in this embodiment, the walls PLA, PLG, PLF and PLD aremutually separated by spaces ESPC.

FIG. 3 schematically illustrates a switch CMT of the prior art such asthat described in French patent application No. 1161407. (The U.S.counterpart is published as U.S. publication no. 2013/0146873.) Thisstructure will be referred to before returning in detail to thestructure and the manner of operation of the device DIS of FIG. 2.

The switch CMT here comprises an assembly ENS1 in the form of anasymmetric cross. This assembly ENS1 comprises a first arm BR1A and asecond arm BR1B built into a beam PTR, also dubbed “central pointer”, attwo locations EMPA and EMPB respectively situated on two opposite facesof the beam PTR. These two locations EMPA and EMPB are spaced a distanced apart.

The left part of FIG. 3 shows the switch CMT, and more particularly theassembly ENS1 encapsulated in an insulating region RIS while the rightpart of FIG. 3 shows the same assembly after etching of the insulatingregion so as to release the arms BR1A and BR1B as well as the beam PTR.

The assembly ENS1, thus released, therefore extends inside a housing LGresulting from the removal of the insulating region RIS, the two armsBR1A and BR1B being built into the edges BDA and BDB of the housing.

After de-encapsulation of an assembly of this type, there is arelaxation of the stresses, thereby bringing about a residuallongitudinal deformation of the arms bringing about a deviation a of thepointer, here clockwise.

More precisely, if one assumes an arm of constant width Wa, thedeviation a is expressed by the following formula:

$a = \frac{d \cdot L \cdot {L_{0}( {L - L_{0}} )}}{{d^{2}( {{2L} - L_{0}} )} + {\frac{4}{3} \cdot W_{a}^{2} \cdot L_{0}}}$where L0 is the length of the arm after relaxation

L0 is equal to

$\frac{L}{1 + \frac{\sigma}{E}}$where σ designates the residual mean longitudinal stress and E theYoung's modulus of the material (equal to about 130 GPa for isotropiccopper).

The residual mean longitudinal stress σ is determined experimentally onthe basis of measurements performed on test structures exhibitingdiverse values of d and diverse values of Wa. Thus, for 1/d equal to 2μm−1 and Wa equal to 0.5 μm, σ equals about 800 MPa.

By way of indication, for arms 10 microns in length and 0.2 microns inwidth, the deviation of the pointer is of the order of 0.2 microns for aspacing d of 2 microns. For a spacing of 1 micron, the deviation a is ofthe order of 0.3 microns. This is understood for switches annealed at400° with an insulating region RIS of 0.56 microns.

For a line width (arm width) of the order of 0.2 microns, a meanlongitudinal residual deformation of between 0.25% and 0.30% is obtainedfor a line width (width of the arms) of 0.5 microns, 0.20% for a linewidth of 1 micron, and a little less than 0.20% for a line width of 2microns.

This displacement a of the pointer is a parameter which must be takeninto account when placing abutments, if any, in the housing.

On the other hand, in the embodiments of the invention, having regard tothe fact that the structure STR is a symmetric structure, there is nodeviation of the beam PTR during the de-encapsulation of the assembly 1and the configuration illustrated in FIG. 3 is the same before and afterrelease of the assembly 1 in the cavity CV of the housing LGT. Thisfacilitates the definition of the location of the abutments in thecavity in relation to the beam PTR. Stated otherwise the stressesgenerated during the fabrication of the device are circumvented here andthe assembly remains almost or indeed totally invariant whatever thestresses generated in the course of the fabrication method.

Furthermore, since there is no displacement of the beam PTR during therelease of the assembly 1, there is no relaxation of the stresses in thestructure STR and the latter is then stressed in tension after releaseof the assembly 1. In addition, it will be seen that these tensilestresses will facilitate the pivoting of the beam upon the applicationof a potential difference to the structure STR.

Reference is now made more particularly to FIG. 4 to describe in greaterdetail the characteristics of the assembly 1 and especially those of thestructure STR.

This structure STR here comprises a first pair of first arms BR11, BR12.These arms BR11 and BR12 are, as indicated hereinabove, stressed intension. They therefore behave after release of the assembly 1 likesprings under tension. They are moreover built into a first edge of thehousing, in this instance the wall PLA. More precisely, the arm BR11 isbuilt into the wall piece PLA1 and the arm BR12 is built into the wallpiece PLA2.

The structure STR also comprises a second pair of second arms BR21 andBR22. By analogy these two arms BR21 and BR22 are stressed in tensionand are built into a second edge of the housing, in this instance thewall PLF.

More precisely, the second arm BR21 is built into the wall piece PLF1and the second arm BR22 is built into the wall piece PLF2.

The two first arms BR11 and BR12 are fixed by their other end on a firstface F1 of the beam PTR at two first fixing locations EMP11 and EMP12.

Likewise, the two second arms BR21 and BR22 are fixed by their otherend, on a second face F2 of the beam, opposite from the face F1, at twosecond fixing locations EMP21 and EMP22.

The fixing locations EMP11, EMP12, EMP21 and EMP22 are arranged so as todefine for the beam a pivot point O which, when the structure isperfectly symmetric with respect to the axes Ax1 and Ax2, is situated inthe middle of the locations EMP11, EMP12, EMP21, EMP22. In this case,the pivot point O forms a point of symmetry for the structure STR.

Thus, by way of indication, the distance d reckoned along the axis Ax1between the arms BR11 and BR12 and between the arms BR21 and BR22 istypically of the order of a micrometer. The width e2 of the arms is forexample of the order of a micrometer and the width e1 of the beam,reckoned along the axis Ax2, is for example of the order of amicrometer.

So as to further favor the pivoting of the beam, those ends of the armsthat are fixed on the beam are advantageously beveled.

Reference is now made more particularly to FIG. 5 to illustrate a firstcase of operation of the device. In FIG. 5, a potential VA1 is appliedto the wall piece PLA1 and a potential VF2 to the wall piece PLF2 whilethe potentials of the wall pieces PLA2 and PLF1 are left floating.

By way of indication, it is for example possible to apply a voltage VA1of up to a few volts and a zero voltage VF2 (ground).

Therefore, a current flows in the arm BR11 and in the arm BR22. Thisconsequently results, through the Joule effect, in an increase in thetemperature of the arms BR11 and BR22. This temperature increase willinitially help to relax the tensile stresses in the arms BR11 and BR22.In addition, since the arms BR12 and BR21 are stressed in tension, theywill have a tendency to pull the beam towards the walls PLA2 and PLF1,so bringing about a pivoting PVT1 of the beam around its pivot pointtowards the abutment BT1.

Next, after relaxation of the tensile stresses in the arms BR11 andBR22, the heating of these arms will lead to an expansion of the latter,so helping with the pivoting PVT1.

With values of the order of a micrometer for the above-mentionedparameters d, e1 and e2, an arm length of the order of 25 micrometers, abeam length of the order of 30 micrometers and a voltage differenceVA1-VF2 of 118 mV, the current flowing in the arms BR11 and BR22 is ofthe order of 54 mA and leads to a displacement of the end of the beam ofthe order of 240 nm.

In the case where, as illustrated in FIG. 6, this time a potentialdifference VA2 minus VF1 is applied between the wall pieces PLA2 andPLF1, while leaving a floating potential on the wall pieces PLA1 andPLF2, this time a current is made to flow in the arms BR12 and BR21,this time bringing about a pivoting PVT2 in the reverse direction, thatis to say towards the abutment BT2.

The explanation detailed hereinabove relating to the pivoting PVT1 ofthe beam PTR applies of course by analogy for the pivoting PVT2.

This assembly 1 therefore allows a movement in the bilateral plane XY.

A possible application of the invention can consist of a currentlimiter. Indeed, if the wall piece PLG1 is grounded, and in the case ofFIG. 5, where a portion of the integrated circuit is connected betweenthe wall pieces PLA1 and PLF2, the current flowing in the arms BR11 andBR22 originating from this portion of integrated circuit, can then, ifit exceeds a certain threshold, cause the beam to pivot towards theabutment (contact region) BT1. In addition, when the beam PT1 comes intocontact with the abutment BT1, a part of the current exits through theabutment BT1 and the wall PLG towards ground, thereby de facto limitingthe current flowing in the arms BR11 and BR22, and consequently in thecorresponding portion of integrated circuit.

It is also possible to limit the current in another portion ofintegrated circuit not operating simultaneously with the first portionof integrated circuit, by this time connecting this other portion to thewall pieces PLA2 and PLF1. The limitation of the current will then beeffected via the abutment BT2.

FIG. 7 illustrates another embodiment of the assembly 1. In thisembodiment, the beam PTR is symmetric with respect to the structure andcomprises two beam pieces PTR1 and PTR2. Two abutments BTA and BTB arerespectively disposed facing and some distance from the ends of the beampieces PTR1 and PTR2. Conventional means GEN, known per se, are able tocause an electric current to flow in the arms BR11 and BR22 so as tobring about the pivoting of the beam PTR towards the abutments BTA andBTB, thereby making it possible to establish an electrical link betweenthe points A and B. Thus, in this embodiment, the device is a switchwhich is in a state which normally open (“normally off”) in the reststate, and in a closed state (“on”) upon the application of a potentialdifference between the wall pieces PLA1 and PLF2, thereby making itpossible to establish an electrical link between the points A and B.

It will be appropriate to note here that a sufficiently high impedancewill preferably be chosen for the circuit A-B so as to force the currentto pass through the arms BR11 and BR12 even when the ends of the beamsPTR1 and PTR2 are in contact with the abutments BTA and BTB.

It is also appropriate to note that if, in the embodiments of FIGS. 4, 5and 6, the abutments BT1 and BT2 were built directly into a wall of thehousing, it is possible, in the embodiment of FIG. 7, that theseabutments are held fixed in the housing by vias, as illustrated forexample in FIG. 8, linking this abutment BTA to a lower metallization bya via V20.

Reference is now made more particularly to FIGS. 9 and 10 to illustratea mode of fabrication of an exemplary embodiment of a device accordingto the invention. It is assumed in these figures that the assembly, aswell as the abutments, are produced at the metallization level M3 (Metal3).

It is then seen (FIG. 9) that use is made of the level V2 of vias 2between the metal level 2 and the metal level 3 and the level V3 of vias3 between the metal 3 and the metal 4 to form the lateral walls of thehousing and form a “protection” wall for the oxide etching which willfollow and allow the de-encapsulation of the assembly and variousabutments.

Moreover, the structure STR and the beam of the switch and also thefixed part, in this instance the abutment or abutments, are produced atthe level of the metal 3.

The switch DIS, and especially the assembly are produced by usingconventional steps for metallization level and vias fabrication. Moreprecisely, as illustrated in FIG. 9, after making the metal level M2 andvia level V2, the assembly, represented here dashed for the sake ofsimplification, is produced in a conventional manner by etching theunderlying oxide and depositing metal, in this instance copper, in thetrenches. Next, the assembly is covered with oxide and the metallizationlevel M4 is produced thereafter.

After formation of a conventional nitride layer C1 on the metal level 4,a comb is made in this metal level 4 so as to form the orifices OR ofthe cap CPT.

Next, an isotropic dry etching is undertaken followed for example by awet etching for example with hydrofluoric acid, so as to eliminate theinsulating region (oxide) encapsulating the assembly as well as thevarious abutments and thereby produce the cavity of the housing LGT.

Next, a non-compliant oxide deposition is undertaken so as to form alayer C2 plugging the orifices OR.

Of course, what has just been described for the metal levels M2, M3, M4can be generalized to the metal levels M_(i)−1, M_(i), M_(i+1).

The conventional method for producing the various higher metallizationlevels is continued thereafter.

In certain embodiments, such as for example those illustrated in FIGS. 4to 6, at least one of the walls of the housing can comprise an opening.In this case, and although not indispensable, it is particularlyadvantageous, as illustrated in FIG. 11 in which for the sake ofsimplification only the interconnection part RITX (BEOL) of theintegrated circuit has been represented, to make provision, facing theopening OUV of a wall, for example the wall PLG of the housing LGT, fora means, here a plate PLQ, external to the housing LGT and configured soas to form an obstacle to a diffusion of fluid, especially thede-encapsulation fluid, out of the housing through the opening OUV. Thismakes it possible to limit the diffusion of the de-encapsulation fluidout of the housing so as to minimize the risk of this fluid degradingother parts of the integrated circuit, such as for example transistorsproduced in the exterior and interior vicinity of the housing.

In the embodiment of FIG. 11, the plate is produced at the metallizationlevels M2, M3 and M4 and at the levels of vias V2, V3. The space betweenthe opening OUV and the plate PLQ can for example vary between 0.12 and1 micron while the thickness of the plate, reckoned in the X direction,can vary between 0.2 and 1 micron. Thus, as illustrated in FIG. 12, thede-encapsulation fluid FL penetrates into the housing through theorifices OR of the cap found CPT and the fluid also propagates outsideof the housing LGT through the opening OUV so as to remove theinsulating material RIS disposed between the wall PLG and the plate PLQ.On the other hand, the diffusion of the fluid out of the housing throughthe opening OUV is impeded by the plate PLQ.

It is however possible, as illustrated in FIG. 13, that in anembodiment, provision is made for a metallization 3 passing through anopening OUV made in a wall of the housing LGT, for example the wall PLG,so as to contact an abutment BT and convey an electrical signal.

As illustrated in FIG. 14 which is a section cut on the line IV-IV ofFIG. 13, the wall PLG in which the opening OUV is made extends, justlike the wall PLD, over the three metallization levels M2, M3 and M4 andthe two levels of vias V2 and V3.

The opening OUV is delimited in the direction D1 (vertical direction) bya first portion of the wall PLG situated at the upper metallizationlevel, in this instance a part of the cap CPT, and by a second wallportion situated at the lower metallization level (the metal level M2)formed here by a portion of the floor wall PI.

The opening OUV is delimited in a second direction perpendicular to thefirst direction (in this instance the horizontal direction) by a thirdand a fourth wall portion extending opposite one another on theintermediate metallization level M3 and on the two levels of vias V2 andV3 flanking this intermediate metallization level.

More precisely, the third wall portion comprises a portion PV20 situatedat the via level V2 surmounted by a portion of metallic track PM30surmounted by another portion PV30 situated at the via level V3.

Likewise, the fourth wall portion comprises a portion PV21 situated atthe via level V2 surmounted by another portion of metallic track PM31surmounted by a portion PV31 situated at the via level V3.

In addition, the through metallization 3 extends at the metallizationlevel M3 while being some distance from the metallic portions PM30 andPM31, that is to say while being electrically insulated from the wallPLG.

Here again the integrated circuit CI comprises a metallic plate PLQ(FIG. 13 and FIG. 15) built into the metallization 3. This plate PLQ isdisposed facing the opening OUV and consequently here extends over thethree metallization levels M2, M3, M4 and the two levels of vias V2, V3.That said, this plate could also overhang the opening and consequentlyextend over additional metallization levels and additional levels ofvias.

More precisely, as illustrated in FIG. 15 which is a section cut on theline XV-XV of FIG. 13, the plate PLQ comprises a lower metallic portionPLQ2 produced at the metal level M2, a portion PLQV2 produced at the vialevel V2, two metallic portions PLQ30 and PLQ31, produced at themetallization level M3 and flanking the metallization 3. In practice,the metallization 3 and the portions PLQ30 and PLQ31 form one and thesame metallic part.

The plate PLQ furthermore comprises a metallic portion PLQV3 produced atthe via level V3 and finally a metallic portion PLQ4 produced at themetal level M4.

The plate PLQ is some distance from the opening OUV, so as not toshort-circuit the metallization M3 with the floor wall PI and the capCPT.

In fact, the plate PLQ of FIG. 15 is analogous to the plate PLQ of FIG.11 except for the difference that it is traversed by the metallization3.

In addition, in a manner analogous to what has been describedhereinabove with reference to FIG. 13, during the de-encapsulation ofthe assembly 1 of the abutment BT and of the metallization 3, thede-encapsulation fluid FL also propagates outside of the housing LGTthrough the opening OUV so as to remove the insulating material RISdisposed between the wall PLG and the plate PLQ but its diffusion isimpeded by the plate PLQ (FIG. 16).

Of course, the external means may be different from a plate and may befor example a tunnel built into the wall PLG around the opening OUV asdescribed in French patent application No. 13 50 161 (and U.S.counterpart application Ser. No. 14/148,884).

What is claimed is:
 1. A method of forming an integrated circuit chipwith a switching device, the method comprising: providing asemiconductor substrate; forming back-end-of-line metallization over thesemiconductor substrate, the back-end-of-line metallization including aplurality of levels of metal, each level of metal extending in arespective plane parallel to and spaced from an upper surface of thesemiconductor substrate; and forming the switching device within acavity in the back-end-of-line metallization, the switching devicecomprising a beam held by a structure at a pivot point and a contactdevice extending into the cavity adjacent to the beam, wherein: thebeam, the structure and the contact device are formed from a same levelof metal of the plurality of levels of metal, the switching device isenclosed in a housing, the contact device is built into a sidewall ofthe housing, the structure comprises a first arm, a second arm, a thirdarm, and a fourth arm, the first arm and the second arm are disposed ona first side of the beam, and the third arm and the fourth arm aredisposed on a second side of the beam, the first side of the beam beingopposite to the second side of the beam, the first arm is aligned withthe third arm, and the second arm is aligned with the fourth arm, thefirst arm is electrically connected to the fourth arm, and the secondarm is electrically connected to the third arm, and the beam isconfigured to pivot in a first direction when a first voltage is appliedto the first arm and a second voltage is applied to the fourth arm, andthe beam is configured to pivot in a second direction when a thirdvoltage is applied to the second arm and a fourth voltage is applied tothe third arm.
 2. The method according to claim 1, wherein forming theswitching device within the cavity comprises: forming the housing frommetal layers of the plurality of levels of metal and via layers of theback-end-of-line metallization, the housing enclosing the cavity andincluding an opening; and removing dielectric material from within thehousing, wherein the dielectric material is removed by using an etchantintroduced via the opening.
 3. The method according to claim 2, whereina barrier region is disposed outside the housing and serves as anobstacle to prevent the etchant from diffusing out of the housingthrough the opening while removing the dielectric material.
 4. Themethod according to claim 2, wherein at least one wall of the housingcomprises a through opening via through which an electrical contact ismade to the structure, and wherein a barrier region disposed outside thehousing serves as an obstacle to prevent the etchant from diffusing outof the housing through the through opening while removing the dielectricmaterial.
 5. The method according to claim 2, wherein: the housing andthe switching device are produced within a first metal layer of theplurality of levels of metal, a second metal layer of the plurality oflevels of metal, a third metal layer of the plurality of levels ofmetal, a first via layer of the via layers of the back-end-of-linemetallization, and a second via layer of the via layers of theback-end-of-line metallization and wherein the cavity is defined in partby a first conductive feature of the first metal layer, a first via ofthe first via layer, and a second via of the first via layer, andwherein the first conductive feature extends from the first via to thesecond via, and the first conductive feature contacts each of the firstvia and the second via.
 6. The method according to claim 1, furthercomprising forming a plurality of transistors in the semiconductorsubstrate prior to forming the back-end-of-line metallization, whereinforming the back-end-of-line metallization comprises connecting theplurality of transistors into a circuit.
 7. The method according toclaim 1, wherein the structure is X-shaped and substantially symmetricalwith respect to the beam.
 8. The method according claim 1, wherein thestructure is stressed in tension in the absence of a potentialdifference applied to the structure.
 9. A method, comprising: forming aninterconnect region over a semiconductor substrate, the interconnectregion comprising a plurality of metallization layers, eachmetallization layer being separated by an insulating layer; and forminga switching device in the interconnect region from the plurality ofmetallization layers, the switching device comprising an assembly in acavity of a housing, the assembly comprising a beam held by a structurebuilt into the housing, the beam and the structure being electricallyconductive and formed from a same layer of metallization of theplurality of metallization layers, wherein the structure comprises afirst plurality of arms disposed on a first side of the beam and asecond plurality of arms disposed on a second side of the beam, thefirst side being opposite to the second side, wherein the beam, thefirst plurality of arms, and the second plurality of arms are completelyformed of metal of the same layer of metallization in which the beam isformed, and wherein a first arm of the first plurality of arms directlycontacts the beam at a first location, a second arm of the firstplurality of arms directly contacts the beam at a second location, afirst arm of the second plurality of arms directly contacts the beam ata third location, and a second arm of the second plurality of armsdirectly contacts the beam at a fourth location, and each of the firstlocation, the second location, the third location, and the fourthlocation is a different location of the beam.
 10. The method accordingto claim 9, wherein the structure is X-shaped and substantiallysymmetrical with respect to the beam, and a major axis of the beam isperpendicular to a respective major axis of each of the first pluralityof arms and the second plurality of arms.
 11. The method according toclaim 9, further comprising: forming the housing from the plurality ofmetallization layers, the housing enclosing the cavity; and forming anopening in a wall of the housing.
 12. The method according to claim 11,further comprising removing dielectric material from within the housingto form the cavity, wherein the dielectric material is removed by usingan etchant introduced via the opening.
 13. The method according to claim11, further comprising forming a metal plate in the interconnect regionproximate to the opening.
 14. The method according to claim 13, furthercomprising forming a conductive trace that passes through the metalplate and the opening and contacts the structure.
 15. A method,comprising: forming a first metal layer over semiconductor substrate;forming a second metal layer over the first metal layer; forming a thirdmetal layer over the second metal layer, wherein a plurality of firstvias electrically connect first conductive features of the third metallayer to one or more conductive features of the second metal layer, andwherein a switching device is formed by second conductive features ofthe third metal layer, the switching device comprising an assembly, theassembly comprising a beam held by a structure; forming a fourth metallayer over the third metal layer, wherein a plurality of second viaselectrically connect one or more conductive features of the fourth metallayer to the first conductive features of the third metal layer, andwherein a housing is formed by the one or more conductive features ofthe second metal layer, the first conductive features of the third metallayer, the one or more conductive features of the fourth metal layer,the plurality of first vias, and the plurality of second vias, whereinthe switching device is disposed inside the housing, wherein a sectionof the housing that is formed by the fourth metal layer comprises one ormore openings over the switching device, and wherein the assemblyextends from a first sidewall of the housing to a second sidewall of thehousing, the first sidewall being opposite to the second sidewall; andperforming an etching process through the one or more openings to removeinsulating material inside the housing surrounding the switching deviceand form a cavity in the housing, the cavity being defined in part by afirst conductive feature of the one or more conductive features of thesecond metal layer, a first via of the plurality of first vias, and asecond via of the plurality of first vias, wherein the first conductivefeature of the one or more conductive features of the second metal layerextends from the first via of the plurality of first vias to the secondvia of the plurality of first vias, and wherein the first conductivefeature of the one or more conductive features of the second metal layerphysically contacts the first via of the plurality of first vias and thesecond via of the plurality of first vias.
 16. The method according toclaim 15, further comprising: depositing an insulating layer over thefourth metal layer, the insulating layer extending into the one or moreopenings.
 17. The method according to claim 15, wherein the etchingprocess comprises an isotropic dry etching process followed by a wetetching process.
 18. The method according to claim 17, whereinhydrofluoric acid is used in the wet etching process.
 19. The methodaccording to claim 15, wherein the structure is X-shaped andsubstantially symmetrical with respect to the beam.
 20. The methodaccording to claim 15, wherein the structure is stressed in tension inthe absence of a potential difference applied to the structure.